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Common Stock - Additional Information (Detail)
$ / shares in Units, $ in Millions
 6 Months Ended
Sep. 11, 2018
$ / shares
shares
Aug. 14, 2018
USD ($)
$ / shares
shares
Aug. 08, 2018
shares
Mar. 31, 2019
USD ($)
$ / shares
shares
Sep. 30, 2018
$ / shares
shares
Class of Warrant or Right [Line Items]          
Warrants term       5 years  
Warrants of common stock exercise price | $ / shares       $ 0.004  
Maximum percentage of stock pertaining to restrictions       24.90%  
Extended term of outstanding warrants expiration period       5 years  
Warrants of common stock expiration date       Sep. 30, 2023  
Warrants to purchase shares of common stock       250,000  
Common stock, stock split       Effected a 2.5-for-1 stock split  
Stock split ratio     2.5    
Common stock, shares authorized     125,000,000 125,000,000 125,000,000
Preferred stock, shares authorized     5,000,000 5,000,000 5,000,000
Stock issued during period, shares, new issues 1,344,500        
Common stock, no par value | $ / shares       $ 0 $ 0
Common stock, warrants issued       6,780,297 10,614,990
IPO [Member]          
Class of Warrant or Right [Line Items]          
Stock issued during period, shares, new issues   9,630,000      
Common stock, no par value | $ / shares        
Shares issued, price per share | $ / shares   $ 12.00      
Gross proceeds of initial public offering | $   $ 115.6   $ 124.2  
Net proceeds from initial public offering | $       111.7  
Underwriting discounts and commissions | $       8.7  
Offering costs | $       $ 3.8  
Underwriter Options [Member]          
Class of Warrant or Right [Line Items]          
Common stock, warrants issued   1,444,500      
Purchased Directly From Company [Member]          
Class of Warrant or Right [Line Items]          
Stock issued during period, shares, new issues 723,985        
Purchased Directly From Selling Shareholders [Member]          
Class of Warrant or Right [Line Items]          
Stock issued during period, shares, new issues 620,515        
Firm Shares and Option Shares [Member]          
Class of Warrant or Right [Line Items]          
Shares issued, price per share | $ / shares $ 12.00